In many cutting operations which utilize abrasive wheels, both thinness and rigidity or stiffness are essential. Examples of such cutting operations are the dicing, slicing, scribing, slotting, and squaring, which are involved in the processing of silicon wafers and so-call pucks made of an alumina-titanium carbide composite, for the electronics industry in general and the computer industry in particular. As is well known, silicon wafers are processed for integrated circuits while alumina-titanium carbide pucks are utilized to fabricate flying thin film heads for writing (recording) and reading (playing back) information magnetically stored in computers.
The alumina-titanium carbide used to form the pucks is highly pure. The pucks are preferably formed by hot-pressing into discs 2 or 3 inches in diameter and typically about 3/16 of an inch thick. The resulting bodies are extremely hard and therefore very difficult to shape, which necessitates the use of diamond grinding and cutting wheels to further process discs. Because these hot-pressed pucks or discs typically contain unacceptable pits and scratches, a 2 to 3 mil coating of alumina is deposited on the puck and polished to the desired finish.
The circuitry for thin film heads is built on the aforedescribed substrate, by first polishing the surfaces of the so-called puck followed by chemical or metal vapor deposition and photolithography treatments. The materials deposited are e.g. alumina and copper. The pucks or wafers are then overcoated with alumina to protect the newly formed circuits followed by lapping of the alumina coating to precise shape and thickness. Enough of the alumina coating is removed, in predetermined locations on the puck, to expose copper to be used as electrical connectors in the final product.
Most of the remaining steps involve the shaping and separating of the thin film heads which are done preferably with diamond or cubic boron nitride (CBN) abrasive wheels. Usually the ceramic substrate, or puck in the case of thin film heads, is usually round, thus the first step is "squaring off" which involves cutting off of the round edges of the puck so that the ceramic substrate will fit into the process equipment. The squared off puck is slotted along one axis to define scribe lines between each row of heads. The scribe lines penetrate the hard alumina coating and the underlying circuits built into the surface of the puck. To avoid thermal and mechanical stress or damage to the circuit lay, scribing is done at a slow rate with fine grit diamond cutting blades. This operation requires very parallel and accurate cuts in order to prevent chipping which can ultimately cause damage to the thin film heads. For this reason the industry carries out this operation with a gang of thin diamond abrasive contain cut-off wheels or blades i.e. several diamond cut-off blades mechanically joined together with spacers of accurately predetermined thickness located between each cutting blade or wheel.
Once the thin film head circuits have been delineated by scribing, the remainder of the thickness of the substrate is cut through again using a gang saw arrangement of diamond blades or wheels and spacers. The result is several accurately cut bars, each of which contains 5, 6, or more, thin film head circuits depending on the size of the original puck. These bars are then lapped to remove the excess substrate material which remains after the scribing and slicing steps set out above. The bars may or may not be lapped depending on whether or not excess substrate material is remaining.
Once the bar is lapped it is mounted in a cartridge so that the air bearing surfaces, called rails and bleed slots, can be cut into the tops of individual heads. First the rails are cut over the alumina covered head circuits, again using a gang set-up of diamond cutting blades and spacers. Then a wider and shallower plateau is cut between the rail channels. The rails and bleeding slots are cut to form the aerodynamic surfaces that allow the thin film heads to fly, thus they must be cut with extreme precision with respect to the correct depth and width.
The next to the last step in preparing the actual head for a flying thin film head is separating the several heads contained in a bar or row. Again in this step of the process the cutting to separate each individual circuit (head) must be done with unfailing accuracy in order to avoid destroying or damaging the heads. As in some of the preceding steps, this operation is generally carried out using a gang of diamond saw blades or wheels. This next to last operation also requires extreme precision of cut.
The final step is the lapping of each individual head to achieve precise throat height and to bevel or ramp the ends of the rails, the throat being the trough between the rail and bleed slot discussed above
For the several aforedescribed steps involving slicing, parting, etc. of pucks with gang saws it is apparent that these cuts must be very accurate in order to avoid damage to the heads being produced. The basic material i.e. alumina-titanium carbide is itself expensive, with the value added as a result of the many steps greatly increasing the cost of a given puck or disc of alumina-titanium carbide. The cuts made by gang saws in processing substrates like alumina-titanium carbide and silicon substrates for thin film heads and integrated circuits respectively, must be made accurately to avoid excess waste of materials and damaged to thin film heads and integrated circuit substrate pieces. In an effort to minimize these costly losses the industry uses gang saw arrangements made up of saw blades that are as stiff as possible and as thin as practical. These two characteristics of the saw blades are obviously contradictory; the thinner the blade the less stiff the blade will be. However, the industry has compromised by using conventionally shaped blades that are a little thicker than desired and not quite as stiff as would be optimum, ganged with precisely sized spacers between the blades. The spacers are smaller in diameter than the blades and are composed of hard rigid materials like steel or bonded tungsten carbide. The wheels are conventionally shaped straight wheels i.e. wheels that are of uniform thickness from the wheel's arbor hole to its periphery.
It is a principal objective of the present invention to overcome the chipping and inaccurate cuts which occur with the presently used straight wheels gauged with spacers.